A variety of vises are used to hold workpieces during machining operations. These vises must be secured to the machine bed and firmly hold the workpiece immobile against the machine tool force. At the same time, the vise must not exert excessive force on the workpiece which would distort the surface being machined. The vise must also not bend or distort, making precision machining impossible.
These vises should also be quickly adjustable, cleanable and allow the machinist to easily relate to drawing dimensions, tolerances and finish requirements. Set up time is a significant cost of machining operations as is removal and cleanup time. Reorientation of the workpiece during machining should be minimized to reduce cost and prevent confusion of drawing requirements.
Prior vises have generally been of two types. The first and older type, provides a support structure with a fixed jaw on one end with a crank driven threaded shaft driving a moveable jaw on the other end in grooves in the structure. This type is simple in construction, but required a heavy support structure (taking axial and bending clamping loads), a heavy threaded shaft (taking compression loads without buckling) and grooves with small tolerances in order to maintain dimensional stability. Set up required fixing the vise to the machine bed and cranking to accept and clamp the workpiece. Reorientation of the workpiece required replacement on the machine bed in many cases if a moveable jaw was used as the drawing reference or reorientation if the fixed jaw was used as the drawing reference surface. Although options such as hydraulic cranking and removable jaw plates reduced these problems, the vise remains heavy and subject to distortion by axial and bending clamping forces.
A more recent vise (supplied by KURT Manufacturing) retains the relative positions of the crank, moveable and fixed jaws, but extends the threaded shaft to the fixed jaw and provides a new offset interface between the moveable jaw and shaft. The new interface deflects a portion of the clamping force to hold the moveable jaw on the support structure. The objective of this force deflection is to improve dimensional precision by not allowing jaw movement within (the previously described) groove.
However, this force deflection adds additional forces tending to bend the threaded shaft and the supporting structure. It also requires that the portion of the exposed structure which mates with the moveable jaw be kept clean. Drit or chips may jam the moveable jaw, or worse, damage the mating surfaces under the deflected force, destroying dimensional precision.
Therefore, although the more recent vise design offers advantages over the older design, the problems of weight, costly setup, disassembly, reorientation and cleaning time remain. In addition, new problems of inability to maintain dimensions when loose and increased risk of damage by dirt and chips has been observed.
Prior vises did not allow clear access from the top to bolt the units on a machine. These vises could only be bolted down from the bottom or by means of side clamps. This made it practically impossible to gang several vises side by side on a machine; unless they were first assembled up-side down on a platen. Removal of the vise for clean-up or repair required the removal of the entire gang.
Numerically controlled machinery is commonly programmed along cartesian coordinates. The axes zero reference is usually indicated as the lower left corner of the workpiece on the blueprints. If the operator is not provided with a stable reference point on the vise which is located on his side of the workpiece, he must either read the blueprint upside down or convert all given dimensions by translation to a stable reference point on the vise. Either one of these palliative measures yield values which are no longer consistent with the data used to program the machine.